Gulf of Maine Seasonal Sea Surface Temperature Update
Seasonal Patterns in Sea Surface Temperatures
About the Updates:
Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal updates about conditions in the Gulf of Maine.
Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.
The Gulf of Maine Region
For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 1), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous seasonal and annual reports that scientists at GMRI have produced.
Fall Highlights
For this seasonal report we present an analysis of SST for fall (September 1, 2023 - November 30, 2023). During this season, the average SST for the Gulf of Maine was 57.25°F, making it the 14th hottest fall on record for the period of 1982-2023 — the period over which the satellite data used are available. This seasonal average temperature is 0.72°F above the 1991–2020 climatological reference period (CRP) fall average of 56.53°F.
Weekly Temperatures
Table 1 highlights how the SST for each week this fall compares to the 1991-2020 CRP for the area shown in Figure 1. The observed SST, long-term average SST, and SST anomalies (i.e., departures from the long-term average SST) are shown.
fall average SST was on average 0.72°F or more above normal during the fall, with weekly averaged SST anomalies ranging from -1.79°F to +3.85°F.
| Table 1. Weekly Average Sea Surface Temperatures - Fall | |||
| (September 1, 2023 - November 30, 2023) | |||
| One-Week Period | Observed Temperature | Climatological Average | Temperature Anomaly |
|---|---|---|---|
Sep 01 - Sep 02 |
63.3°F (17.4°C) |
62.7°F (17.0°C) |
0.7°F (0.4°C) |
Sep 03 - Sep 09 |
64.4°F (18.0°C) |
62.3°F (16.8°C) |
2.2°F (1.2°C) |
Sep 10 - Sep 16 |
64.7°F (18.2°C) |
61.6°F (16.4°C) |
3.1°F (1.7°C) |
Sep 17 - Sep 23 |
59.3°F (15.2°C) |
60.8°F (16.0°C) |
-1.4°F (-0.8°C) |
Sep 24 - Sep 30 |
58.3°F (14.6°C) |
59.8°F (15.4°C) |
-1.5°F (-0.8°C) |
Oct 01 - Oct 07 |
58.5°F (14.7°C) |
58.7°F (14.8°C) |
-0.2°F (-0.1°C) |
Oct 08 - Oct 14 |
57.9°F (14.4°C) |
57.6°F (14.2°C) |
0.3°F (0.2°C) |
Oct 15 - Oct 21 |
57.6°F (14.2°C) |
56.3°F (13.5°C) |
1.3°F (0.7°C) |
Oct 22 - Oct 28 |
57.4°F (14.1°C) |
55.1°F (12.8°C) |
2.3°F (1.3°C) |
Oct 29 - Nov 04 |
55.8°F (13.2°C) |
53.9°F (12.2°C) |
1.9°F (1.0°C) |
Nov 05 - Nov 11 |
53.6°F (12.0°C) |
52.8°F (11.6°C) |
0.8°F (0.4°C) |
Nov 12 - Nov 18 |
51.7°F (10.9°C) |
51.8°F (11.0°C) |
-0.1°F (-0.0°C) |
Nov 19 - Nov 25 |
51.0°F (10.5°C) |
50.8°F (10.4°C) |
0.2°F (0.1°C) |
Nov 26 - Nov 30 |
50.2°F (10.1°C) |
49.9°F (9.9°C) |
0.3°F (0.1°C) |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | |||
| Climatological Reference Period: 1991-2020. | |||
Monthly Statistics
Table 2 shows monthly average SST for fall 2023; each month was within 1°F or more above the 1991-2020 CRP. October showed the largest deviation from the long-term climatological average, with an average SST anomaly of 1.08 °F, making it the 12th warmest October on record. September and November were cooler at 0.6 & 0.5°F above the long-term average—coming in as the 14th and 16th warmest September and November on record, respectively.
| Table 2. Monthly Average Sea Surface Temperatures - Fall | ||||
| (September 1, 2023 - November 30, 2023) | ||||
| Month | Rank (1982-2023) | Observed Temperature | Climatological Average | Temperature Anomaly |
|---|---|---|---|---|
September |
14 |
61.8°F (16.6°C) |
61.2°F (16.2°C) |
0.6°F (0.3°C) |
October |
12 |
57.7°F (14.3°C) |
56.7°F (13.7°C) |
1.1°F (0.6°C) |
November |
16 |
52.2°F (11.2°C) |
51.7°F (11.0°C) |
0.5°F (0.3°C) |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | ||||
| Climatological Reference Period: 1991-2020. | ||||
How Does this Fall Compare to the Past?
2023 is the 14th warmest fall season observed in the Gulf of Maine during the 41 years we have satellite data to analyze, a departure fall seasons in recent years, which experienced well-above average SSTs.
Seasonal Trends and Long-Term Global Context
The Gulf of Maine is an area of particular interest to the scientific community because of the remarkable rate of warming it has experienced in recent years coupled with its importance as a major driver for the regional economy.
Figure 3 illustrates the average fall temperature anomaly for each year in the Gulf of Maine since the beginning of the satellite record in 1982 overlaid with long-term SST anomaly trends for the Gulf of Maine (orange) and global oceans (blue) overlaid. The fall rate of warming for the Gulf of Maine (1.11°F per decade) is roughly 4x as fast as the warming rate for oceans globally (0.26°F per decade). The fall SST anomaly for the Gulf of Maine in 2023 was 2.75°F cooler than that from 2022, the largest year-over-year decline in fall temperatures in the satellite record. Despite the sizable year-over-year change, fall 2023 remained warmer than 28 of the 29 fall seasons prior to 2010, consistent with the observed long-term warming trend in the region.
The unprecedented levels of warmth over the past decade or so are consistent with what researchers describe as a distinct regime shift in terms of the major influences on SSTs in the Gulf of Maine. The drivers of this (e.g., a potential weakening of the Atlantic Meridional Overturning Circulation, widening of the Gulf Stream, changes in the characteristics of the Labrador Current) have been well-documented in the peer-reviewed literature, including through research by GMRI scientists.
Observed SSTs are also influenced by atmospheric weather patterns which can act to amplify warming or cooling of surface waters. Sustained periods of low cloud cover and the consequent direct sunlight can rapidly warm the ocean at the surface. Steady winds can act as a fan, advecting heat away from the ocean and cooling the surface. Strong winds and storm systems may also lower SST through mixing, which can bring cooler water from depth closer to the surface.
In September 2023, extratropical storm Lee traversed the Gulf of Maine, which weakened from hurricane strength as it crossed over Georges Bank on September 16. The impacts of this storm on the region’s SSTs can be seen in Table 1. Similar storm crossings have occurred in the recent past, including in 2019 when Hurricane Dorian passed through the Gulf of Maine after working its way up the US East Coast. Both years had some of the fewest fall heatwave days seen in the past two decades (2019: 0 days, 2023: 6 days).
Marine Heatwave Conditions
The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event.
Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 7% of this fall. September was the only month this fall where SST was above the threshold of a MHW, ultimately exhibiting these anomalously warm conditions for a total of six days. SSTs for the remainder of the season remained closer to the long-term average, even dipping below that climatological average for almost three weeks from late September into early October.
Presenting SST conditions in terms of anomalies ( Figure 5 ) as opposed to absolute values ( Figure 4 ) illustrates in greater detail the magnitude of MHW conditions throughout the fall. The most extreme daily SST anomalies for fall 2023 occurred towards the start of September, with temperatures building to over 3°F above the climatological average above the climatological average before rapidly dropping to cooler for the remainder of the fall. This rapid drop in SST coincided with Hurricane Lee’s passage through the area, demonstrating how atmospheric conditions can alter ocean surface conditions.
Heatmap of Temperature Anomalies and Heatwave Events
Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 6), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.
SST anomalies in the Gulf of Maine this fall were lower than in any season since mid-2019. Fall SST in the previous 3 years had been noteworthy for their extended MHW conditions, part of the long-term trend of unseasonably warm fall since 2012 (Figure 2). The relatively mild fall in the Gulf of Maine this year is a contrast to the 2023 spring and summer seasons—which were the 2nd & 8th warmest on record—and stands in stark contrast to fall SST conditions in the broader North Atlantic region (see Figure 10).
Spatial Distribution of Seasonal Anomalies
From an aerial perspective, the Gulf of Maine experienced mild above-average SSTs during fall of 2023. In general, conditions were relatively mild, exhibiting seasonally-averaged SST anomalies that did not deviate beyond +/- 3°F from the long-term average. There was an east-to-west gradient in seasonally averaged SST anomalies within the Gulf of Maine, potentially representing the influence of the anomalously cool surface water (depicted by the deep blues in Figure 7) entering the study region through the Northeast Channel. The highest seasonally averaged SST anomaly in the Gulf of Maine was 3.05°F - located near Penobscot Bay.
Monthly Temperature Anomalies
Average monthly SST anomalies are shown in Figure 8. During the month of September, the Gulf of Maine experienced above-average SSTs with the warmest anomalies concentrated along the shallower coastal areas to the west. Colder than average temperatures were present near the Northeast Channel to the east, where the waters are deeper. In October the pattern persisted, but with fewer below-average temperatures in the Northeast Channel area. By November the limited warming of October had reversed, with cooler anomalies again present near the Northeast Channel as well as to the north towards the Bay of Fundy. Across all months a large area of colder than average SST anomalies was present to the southeast of the Gulf of Maine. This area of colder water exhibited the coldest SST anomalies during October. The cold patch appeared to move westward over the course of the fall season, along the edge of the continental shelf.
Data Sources:
NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html.
NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.
Citing This Work
If you would like to cite this report, please use:
Gulf of Maine Research Institute. 2022. Gulf of Maine Warming Update: Fall 2023